Insulated electrical conductor



Feb. 24, 1942. L. A. BANNON ,0

' INSULATED ELECTRICAL CONDUCTOR Filed Feb. 25, 1958 LEAD .JHEATH OIL Patented Feb 24, 1942 2,274,031 INSULATED ELECTRICAL CONDUCTOR LewisA. Bannon, Roselle, N. 3., assignor to Standard Oil Development Company, a corporation of Delaware Application February 25, 1938, Serial No. 192,480

e Claims.

" This invention relates to improved insulated electrical conductors and methods of manufacturing same and more particularly it relates to electrical conductors insulated with synthetic oils derived from lower molecular weight aliphatic hydrocarbons. In the construction of insulated electrical con ductors, it is frequently desirable to use an'oil as one of the primary insulating mediums, particularly in the case of cables in which a single or stranded electrical conductor has an outer coating such as a lead sheath, there being an insulating space between the conductor and the sheath; in'such a case, this insulating space is generally filled with an oil alone; small solid objects being used as spacers to keep the conductor properly positioned in the center of the surrounding lead sheath, or else the conductor is wrapped with paper and after covering with a lead sheath, the .insulating oil is forced in under pressure until it has thoroughly impregnated all the paper wrapping and'has filled any interior interstices.

The oil to be used for such purposes must meet various requirements as to certain physical properties in addition to having satisfactory resistivity and other electrical properties. For example, when the conductor is first wrapped with paper and then impregnated with the oil, it is essential that the oil have great penetrating power at the temperature being used for the impregnation and yet it is desirable that the oil become extremely viscous or practically solidified at atmospheric (operating) conditions. Under such circumstances it is desirable to use an oil having a very low V. I. (viscosity index). This V.'I. is a measure of the viscosity-temperature relationship 01 an oil; a high V. 1. oil showsrelatively little change in viscosity for a given change in temperature, but a low V. 1. 011' shows a relatively great change in viscosity .ior a;given change in temperature. This V. I. test is explained in an article entitled,

, "Viscosity Variations of Qils with temperature,

by Dean and Davis, Chem. & Met.,,vol. 36, pg.

618-9 (October, 1929).

On the other hand, when it is desired to use as cable insulation an oil which will not change very much in fluidity or viscosity over a fairly wide temperature range, such as the upper and lower limits of atmospheric temperature, it is desirable to use an oil having substantially higher V. I., such as between the approximate limits of '75 and 120.

According to the present invention, electrical conductors may be insulated with either relatively high V. I. or low V. I. synthetic oils made according to a process which is adaptable to the production of either type of oil, depending upon the intended use. It is preferred to make and use the low V. I. oils, as there has heretofore been a substantial scarcity of materials which are satisfactory for this purpose.

Broadly, the invention comprises treating low molecular weight normally liquid polymers of normally gaseous olefines, particularly iso-olefines, with an acid-reacting halide catalyst of the Friedel-Craits type, such as aluminum chloride, boron fluoride and the like, at a temperature between the approximate limits of -50 C. and 120 0., preferably between about 0 and 100 C. Suitable polymer raw materials include diisobutylene, triisobutylene, or other higher polymers. Similar polymers of other iso-olefines, such as 2-methyl butene-l, may be used, and also vco-polymers, such as those of iso-olefines combined with normal olefines, e. g., a co-polymer of iso-butylene and normal butylene. When these 1 various polymers are treated alone with a catalyst,

the resultant oil has a relatively low V. 1., generally below 10, and they may be as low as'-200 or lower.

Isobutylene is an unsaturated hydrocarbon of the formula CdHB, having one unsaturated linkage between carbon atoms. Accordingly, isobutylene dimer produced from two isobutylene and are the preferred raw materials for the weight polymer raw materials are treatedwith a has asubstantiallyhigher V. I. in the range of molecules has eight carbon atoms; trimer has twelve carbon atoms; tetramer has sixteen carbon atoms; and pentamer has twenty carbon atoms. These may be called the low polymers,

present invention.

0n .the other hand, if these low molecular from up to or more. Theyield and the V. I. of the oil wi depend greatly on the proportion ormonomer and polymer raw material,

as well as upon the temperature and the amount and type of catalyst. Generally the proportion of monomer, such as iso-butylene, should not be more than 3 times the weight of the dimer or other low molecular weight polymer used.

Some general requirements which apply both to the high V. 1. oils and the preferred low V. 1. oils are that they should have a molecular weight between the approximate limits of 300 or 400 and about 5000 and that their Saybolt viscosity at 100 F. should not greatly exceed about 20,000 seconds and preferably should be not more than 5000. Due to their characteristic method 01 manufacture of these oils, they all have a relatively low pour point, e. g. between about and 25' F., because they are wax-free and no -dewaxing is required, even though they may have the high viscosity mentioned above. They have very high penetration and spreading Dower.

The preferred type of oil, namely, the low V. 1. oils, should generally have a Saybolt viscosity of between the approximate limits of 35 and 200 seconds at 210 F. and should generally have a viscosity of over 100 and preferably over 400 seconds at 100 F.

On the other hand, the high V. I. oils can tolerate a substantially higher viscosity at 210 1''., namely, between the approximate limits of 50 and 1000 seconds, while their viscosity at 100 F. will generally not be below 400 and h preferably between about 1000 and 10,000.

As catalyst, it isalsopoasible to use complexes Low V. 1. cable oils Oil characteristics Reactant Catalyst aga Via/100 Via/210 v.1.

Diisobutylene BFI-H;O 10 138.9 39.7 -l4 Do BFa-HsSOa. 0 17,600 173.6 l90 Do Ch 100to 110 352.7 46.6 -34 Do A101; 25 304.6 45.3 -as Do BF: -to 444 50.6 3

Such low V. I. oils produced by polymerizing diisobutylene under the conditions indicated spread over five times more surface than a mineral oilof the same viscosity at 100 F. placed on a highly polished surface for a given length of time. Therefore, these oils are particularly adapted for penetrating into interstices of a iibrous'paper or other wrapping material used in making insulated electrical cables.

Taste 2 Hioh V. 1. cable oils Percent lsobuiyicno Dimer Temp.

Oil characteristics cmlyn va wo Via/210 v.1.

C. H) 0 BF: ,0! m 140 3.3 0 151013.- 11,706 385.2 M 33.3 -l5 AlClL-.. 7,935 1,049 137 33 3 0 Bil-Hi0 0 M 125 50 40 10 +50 5,N1 m 107 of aluminum chloride or boron iluoride or other materials, for instance, a solution of excess boron fluoride in complexes of boron fluoride and water, and boron fluoride and sulfuric acid.

The exact manner of carrying out the polymerization or copolymerization may be varied somewhat. For instance, the catalyst, alone or dispersed in a solvent or diluent, may be added to the polymer or copolymer raw material. such as diisobutylene, alone or in admixture with the mono-isoolefln, such as isobutylene, and/or in the presence of an additional liquid serving as solvent or diluent, such as liquefied propane or butane. When the dimer is to be copolymeriz'ed with the monomer, better control of the reaction is obtained by first dissolving or suspending the ing a product having a narrower molecular weight spread and thereforethe product is more uniform.

The high V. 1. cable oils produced as indicated in Table 2 have good spreading properties and low pour point and are, therefore, superior to natural paraiilnic oil distillates of corresponding viscosity, because the paraiilnie oils generally owe their high V. I. to the presence of waxy constituents which tend to give the oil a relatively high pour point and yet if the bil i's dewaxed in order to produce a satisfactorily low pour point, the V. I. is correspondingly reduced.

For the sake of illustration, several modifications of insulated electrical conductors are shown in the accompanying drawing. 7

Fig. 1 shows a longitudinal view of an electrical conductor insulated with a spiral wrapping of paper impregnated with the preferred synthetic oil, whereas Fig. 2 and Fig. 3 show a longitudinal section and cross-section, respectively, of a cable surrounded by a metal sheath and an intermediate insulating body submerged in the preferred synthetic oil.

Referring to Fig. l, the electric conductor I, surrounded by an outer protective layer, such as lead sheath 2, has an intermediate spiral wrapping of paper 3 which has been impregnated with the preferred synthetic oil insulating medium. In practice, either th paper is impregnated with this oil prior to wrapping around the conductor, or, as in the preferred practice, the dry paper is wrapped around the conductor and covered with a lead sheath and then, after evacuating as much as possibleof the air, the entire paper wrapping is impregnated by forcing hot oil into one end of the cable until it issues at the other end.

Referring to Figs. 2 and 3, electric conductor I is surrounded with an outer protective metal layer, such as lead sheath 2, and by means of any suitable spacing means 4 the conductor is held properly positioned in the center of the lead sheath 2 and then the intervening space between the conductor l and sheath 2 is filled with the preferred synthetic oil insulating medium described in the specification.

In'the appended claims, when the term polymer is used-in describing low molecular weight polymers of iso-olefins, it is intended to also include copolymers of iso-oleflns with normal olefins.

It is not intended that the invention be limited to any of the specific examples or specific embodiments of the invention which have been given merely for the sake of illustration, nor' to any theories given as to the mechanism of the operation of the invention, but only by the appended claims in which it is intended to claim all novelty inherent in the invention as broadly as the prior art permits.

I claim:

1. An insulated electric cable comprising in combination a metallic conductor, a sheath and an insulator member surrounding said conductor within said sheath consisting of a solid insulating member and a submerging insulating oily olefinic polymer produced by polymerization of an isobutylene dimer characaterized by fluidity, by a low pour point below about F., by freedom i'rom wax, by a high penetrating and spreading power, by a molecular weight between the limits of approximately 300 and 5,000 and a viscosity index below approximately 0.

2. An insulated electric cable comprising in combination a metallic conductor, a sheath and an insulator member surrounding said conductor within said sheath consisting of a solid insulating member and a submerslns insulating oily oleflnic polymer produced by polymerization of an isobutylene dimer characterized by fluidity, by a low pour point below about 0 F., by freedom from wax, by a high penetrating and spreading power, by a molecular weight between the limits of approximately 300 and 5,000, by a viscosity index below approximately 0, by a Saybolt viscosity at 210 F. within the range of approximately 35 to 200 seconds and a Saybolt viscosity at F. above 400 seconds.

3. An insulated electric cable comprising in combination a metallic structure, a sheath and an insulating member surrounding said conductor within said sheath consisting of a fibrous material wrapping around said conductor within said sheath and a submerging body of an insulating oily olefinic polymer produced by polymerization 01' an isobutylene dimer characterized by fluidity, by a low pour point below about 0 F., by freedom from wax, by a high penetrating and spreading power, by a molecular weight between the limits of approximately 300 and 5,000 and by a viscosity index below approximately 0.

4. An insulated electric cable comprising in combination a metallic structure, a sheath and an insulating member surrounding said conductor within said sheath consisting of a fibrous material wrapping around said conductor within said sheath and a submerging body of insulating oily ole'flnic polymer produced by polymerization of an isobutylene dimer characterized by fluidity, by a low pour point below about 0 F.,- by freedom from wax, by a high penetrating and spreading power, by a molecular weight between the limits of approximately 300 and 5,000, by a viscosity index below approximately 0, by a Saybolt viscosity at 210 F. within the range of approximately 35 to 200 seconds and a Saybolt viscosity at 100 F. above 400 seconds.

5. An insulated electric cable comprising in combination a metallic structure, a sheath and an insulating member siirrounding said conductor within said sheath consisting of a solid insulating spacer means around said conductor within said sheath and a submerging body of insulating oily olefinic polymer produced by polymerization of an isobutylene dimer characterized by fluidity, by a low pour point belowab'out 0 E, .by freedom from wax, by a high penetrating and spreading power, by a molecular weight between the limits of approximately 300 and 5,000 and by a viscosity index below approximately 0.

- LEWIS A. BANNON. 

